Manufacture of iron blues



Patented June 18, 1935 UNITED STATES PATENT OFFICE 5 ferric potassium ferro-cyanides, and areexempli- MANUFACTURE or men BLUES Samuel Felton Grove, Swarthmore, Pa., assignor toHenry Bower Chemical Manufacturing Company, Philadelphia, Pennsylvania Pa., a corporation of 9 Claims.

This invention relates to the manufacture of colors of the general type commercially known as.

,iron' blues, which are believed to be in the nature of ferric ammonium ferro-cyanides and lied by Prussian blue, bronze blue, Chinese blue, and rnilori blue, as well as by a soluble blue used for laundry purposes. Besides a new and improved process of manufacture, the invention alfords blues with important new characteristics and advantages: in particular, such blues can be made of much softer texture than heretofore so as to grind more easily for the manufacture of printing inks; and so that when bronze blues are ground, they develop their peculiar bronze or red tone more strongly. My blues, moreover, can be made not only to duplicate the purple, bronze, and green tones characteristic of Prussian, bronze "Chinese and milori blues heretofore known, but

also with a new and very pleasing violet tone.

, In the manufacture of iron blues as heretofore practiced, solutions of a (soluble) alkali ferrocyanide and of a (soluble) ferrous salt are brought together in a tank, with agitation, and the refsultant b1uish-white precipitate is oxidized to a darker blue with oxidizing agents, such as dichio'mates, chlorates, chlorine, ferric salts, etc., -etc. The depth. of color and character of the product are .largelydetermined and regulated by the temperature and concentrations of the several solutions, and'by the relative proportions of ferrocyanide, ferrous salt, and oxidizer, as well as by theparticular oxidizer used. The product is washed by decantation several times, until sufli- ,cientl'y free. of soluble impurities, and is then filter-pressed. The filter cake is broken up and dried in tray driers, when it is ready for the grinding or other treatment required for the particular use 'to which it is to be put.

The .color and brilliancy of the finished blue are greatly influenced by the particular alkali in its molecules,-blues containing ammonium or potassium being generally much better than those containing sodium. Generally, sodium ferrocyanide and ferrous sulphate (copperas) solutions areused, and ammonium sulphate is added to the copperas solution to introduce into the blue sufficient ammonium to give it the desired qualities. Theammonium will-enter the molecules of the blue in preference to the sodium; although some sodium is nevertheless present in them, owing to mass action in solution. In any case, great care is necessary in mixing the ferrocyanide and ferrous salt solutions, since if they come together in large. 1iquid.masses, local excess, of oneor the other solution will result in precipitates of varying composition, that are quite different from that desired. Hence the solutions employed should not be too concentrated.

the starting material (ferrocyanide) and the subsequent process are preferably different from those heretofore used. Instead of a freely soluble alkali ferrocyanide, I prefer such as are sparingly soluble (relatively or substantially water-insoluble), owing to the presence of a different base. With such base may be associated any of thealkalies desirable in the-final blue; and the base need not remain in the blue, but may preferably be eliminated in the process of manufacture. For the base may be used any of the metals (well known to chemists) which form relativelyinsoluble double salts with the alkalies, and do not, in reaction with the ferrous salts that may be used, form diluent compounds that cannot be separated (washed or dissolved away) from the blue (or from the ferrous alkali ferrocyanide initially formed) without affecting the same; but for various reasons, I at present prefer the double calcium-alkali ferrocyanides for this purpose. However, other alkaline earth metals may be employed (such as barium) especially when dilution of the blue with their compounds formed in reaction with ferrous salts is not objectionable. Of the cheaper alkalies, potassium and ammonium are preferred as giving much better blues than sodium and I have hereinafter referred to them as the potassium-ammonium class. I have hereinafter explained and illustrated my process in detail with particular reference to calcium-ammonium ferrocyanide; but it is to be understood that calcium-potassium ferrocyanide might be used with equally good results, by merely varying the proportions given in correspondence with its different molecular weight.

-Using a water-insoluble ferrocyanide and. a soluble ferrous salt, I bring them together in water, the ferrous salt in solution, and the ferrocyanide in a finely divided state, suspended or stirred up and dispersed in the water. i In practice, calcium ammonium ferrocyanide as a fine crystalline powder is put into a wooden tankcontaining water which has been rid of dissolved oxygen by boiling. To this is added, with concurrent agitation to keep the ferrocyanide in suspension, a solution of ferrous sulphate, which may contain more or less sulphuric acid (or none), according to the kind of blue to be produced, and

f may also contain a minor amount of sodium chloride,although this is not essential. Agitaa In accordance with the present invention, both l tion is continued until the reaction is completed:

Ca (NH l) 2FBCye +FeSOi=Fe (NHi) 2FeCye+CaSO4 Calcium ammonium ferrocyanide is well known, and is usually prepared according to a react1on such as:

Then, without separating the precipitated calcium ammonium ferrocyanide from the liquor, add solution of ferrous sulphate.

As calcium ammonium ferrocyanide is but slightly soluble in water (only 0.3 to 0.4%), its reaction with the ferrous salt is mainly between solid particles of ferrocyanide and dissolved ferrous sulphate, and hence goes on progressively for some time: i. e., some time is required to complots the reaction, even with the most eflicient agitation; Moreover, the initial reaction between the small amount of dissolved double ferrocyanide and the ferrous salt results in'a coating ofth-e solid ferrocyanide particles by the precipitate initially formed, and this restrains and slows up the further reaction, since the ferrous salt solution must diffuse through this coating to react with the solid double ferrocyanidc. The reaction is self-regulating, so that a substantially uniform product is assured; and this holds true both when the double ferrocyanide itself is used, and when its preparation is combined with its reaction with the ferrous salt, as described above.

Whichever way the reaction between the double ferrocyanide and the ferrous salt is carried out, it

yields a bluish white precipitate of substantially colloidal ferrous ammonium ferrocyanide, approaching the formula Fe(NH4)2FeCye, but containing less NH:= than if entirely of this composi- I tion,-although more than when sodium ferrocyanide and ammonium sulphate are used in accordance with prior practice as described above.

The precipitate forms with the water or solution a slurry that thickens more and more as the reaction proceeds to completion. The vigorous agitation at first employed is preferably moderated as the liquid thickens to the consistency of a slurry, to avoid breaking up its particles. Being 1 only slightly soluble, the calcium. sulphate is precipitated with the ferrous ammonium ferrocyanide, probably intimately mixed therewith in the ultimate discrete particles of the composite precipitate. I

After the reaction and precipitation have been completed, the oxidizer (dichromates, chlorates, etc.) may be added, in the amount and concentration necessary for the kind of "blue desired, as usual in making iron blues. This produces the The blue is then washed free of soluble impurities, including calcium sulphate, excess acid,

and reduced salts from the oxidizer, by decantation. No more washing than usual in the making of iron blues is required. However, the blue settles much more quickly than in ordinary practice, and there is less loss of fine floating particles in the decanted liquor. When the blue is sufficiently free of impurities, which usually requires about four decantations, the slurry is filter-pressed and the filter cake dried as usual. The slurry, however, is less gelatinous than ordinary blues, so that it filters more freely and rapidly, and also dries more quickly.

The exact composition, color, and other physical properties of the initial ferrous ammonium ferrocyanide and of the finished blue are controlled and regulated by the conditions as to temperature, concentrations, and proportions of the various solutions. For example, taking molecular proportions of calcium ammonium ferrocyanide and ferrous sulphate as a basis of reckoning, an excess of of ferrous sulphate may be used for milori blue,20-30% excess for bronze blue, and 50% excess for Prussian blue. For -milori" blue, however, a substantial amount of non-oxidizing acid (e. g., hydrochloric or, preferably, sulphuric) is used in the ferrous sulphate solution; for bronze blue, a less amount of acid; and for Prussian blue little or no acid.

Examples of detailed procedure for particular shades of blue are as follows:

Light milori blue Mix 100' lbs. calcium ammonium ferrocyanide with 175 gal. boiling water in a GOO-gallon tank, V

with vigorous agitation or stirring; and then, while continuing the agitation, run in as quickly as possible a nearly boiling hot (100 C.) solution -of 106 lbs. ferrous sulphate dissolved in 185 gal. water, containing also 23 lbs. of 66 B. commercial sulphuric acid and, preferably, lbs. of commercial sodium chloride. The sodium chloride is not necessary, though I prefer to use it. Hold the temperature at about 100 C. and continue stirring, for about an hour.. However,

the stirring may preferably be moderated after about 15 to 20 min., when the solution has thickv 'ened'enough tobe properly called a slurry, thus avoiding breaking up the'precipitateof ferrous ammonium ferrocyanide and calcium sulphate. This precaution seems to improve the quality of the finished blue somewhat.

After an hours agitation at 100 0., add a solution of'9 lbs. sodium chlorate'in 40 gal. water at 100 0., containing also 10 lbs. of 60 Be. commercial sulphuric acid. Keep hot (about 100 C.) and continue moderate stirring for about longer. Then transfer to a 1200 gallon washing tank, and make up to 1200 gal. by addition of hot' water. decant the supernatant liquor; and repeatthis (making up with water and decanting) four or five times, or until the clear liquor run off is free of acid. This amount of washing will completely dissolve out andwash away the from the blue. After this, the blue is filter-pressed and the filter cake dried in the usual manner. This may be done in tray driers at low temperature e. g., starting at C. and raising the temperature to -70 C. as the blue dries. Overheating should be avoided, as the blue will ignite spontaneously at about 100 C., especially when wet or moist.

Dark Chinese blue Mix 100 lbs." calcium ammonium ferrocyanide Let stand over night andv into 150 gal. water at C. in a GOO-gallon tank, with vigorous agitation or stirring; and then, while continuing the agitation, run in quickly a solution of lbs. ferrous sulphate dissolved in 250 gal. water at 10 0., containing also 43 lbs. of 66 B.'commercial sulphuric acid and 40 lbs. commercial sodium chloride. The sodium chloride is not necessary, though I prefer to use it. Hold the temperature at 70 C. and continue stirring for about two hours. However, the stirring may preferably be moderated after about 15 to 20 min., when the solution has thickened to a slurry, as before.

After two hours agitation at 70 0., and a solution of 12 lbs. sodium chlorate in 40 gal. water at 70 0., containing also 20 lbs. of 66 Bhcommercial sulphuric acid. Hold the temperature at 70 C. with continued moderate agitation for about 45 min. longer. Then transfer to a 1200- gallon washing tank and wash by decantation four or five times, or until the clear liquor run off is free of acid. Then filter-press and dry the blue as usual.

Other blues (Prussian, bronze, and soluble blues) may be made by varying the ingredients and conditions as indicated above, and as well understood by chemists skilled in the making of iron blues. In work on a smaller scale, it may be desirable to protect the hot agitated solutions from oxidation by an atmosphere of illuminating gas or other non-reactive gas above them, although this will not usually be necessary in work on a commercial scale such as described above.

This application is a continuation of my application Serial Number 629,503, filed August 19, 1932.

Having thus described my invention, I claim:

1. An improvement in the making of iron blues, which improvement comprises bringing into reaction together, in water, a dissolved ferrous salt and a suspended sparingly soluble double ferrocyanide of an alkali and a metal which will replace the iron of said ferrous salt.

2. An improvement process according to claim 1 wherein the double ferrocyanide therein mentioned is formed in the Water where its reaction with the ferrous salt afterward takes place, by reaction of a ferrocyanide with an alkali compound.

3. An improvement process according to claim 1 wherein the solution is vigorously agitated until it thickens to a slurry, and thereafter more moderately agitated during further progress of the reaction.

4. An improvement in the making of iron blues, which improvement comprises bringing into reaction together, in water, a dissolved ferrous salt and a suspended sparingly soluble double ferrocyanide of an alkali and an alkaline earth metal.

5. An improvement process according to claim 4 wherein the double calcium alkali ferrocyanide therein mentioned is formed in the water where its reaction with the ferrous salt afterward takes place, by reaction of an alkali ferrocyanide with a salt of an alkaline earth metal and an alkali compound.

6. An improvement in the making of iron blues, which improvement comprises bringing into reaction together, in water, a dissolved ferrous salt and a suspended sparingly soluble double ferrocyanide of an alkali and a metal which will form a sparingly soluble salt with the acid radical of said ferrous salt, and dissolving out this last- .mentioned salt.

'7. An improvement in the making of iron blues, which improvement comprises bringing into reaction together, in water, a suspended double ferrocyanide of calcium and a. member of the ammonium-and-potassium class, and a dissolved ferrous salt reacting therewith to form a sparingly soluble calcium salt, and eliminating this last-mentioned salt.

8. An improvement in the making of iron blues, which improvement comprises bringing into reaction together, in water, a dissolved ferrous salt and a suspended calcium-ammonium ferrocyanide, and dissolving out the calcium salt formed.

9. An improvement in the making of iron blues, which improvement comprises bringing into reaction together, in water, a ferrous salt and a suspended sparingly soluble ferrocyanide containing an alkali and a metal which will interchange with the iron of said ferrous salt, and afterward dissolving out, from the iron-containing ferrocyanide blue, the salt that is formed by substitution for the iron.

SAMUEL FELTON GROVE. 

